"Expanded porphyrins" are large, pyrrole-containing macrocyclic analogues of the porphyrins. Examples of these compounds are porphine, the smaragdyrins, sapphyrins, oxosapphyrins, platyrins, pentaphyrins, hexaphyrins, superphthalocyanines, rubyrins, and texaphyrins. Such molecules are of potential interest because suitably designed systems could act as versatile ligands capable of binding larger metal cations and/or stabilizing higher coordination geometries than those routinely accommodated within the normally tetradentate ca. 2.0 .ANG. radius porphyrin core. The resulting complexes could have important application in the area of heavy metal chelation therapy, serve as contrast agents for magnetic resonance imaging (MRI) applications, act as vehicles for radioimmunological labeling work, or serve as useful photosensitizers for photodynamic therapeutic applications.
The texaphyrins have been found to be useful as MRI contrast agents, as radiation sensitizers and in photodynamic therapy (PDT), as well as having the ability to hydrolytically cleave phosphate esters, including RNA, and to photolytically cleave RNA and DNA. Texaphyrin is considered as being an aromatic benzannulene containing both 18.pi.- and 22.pi.-electron delocalization pathways. See, e.g., Sessler, J. L. et al., Accounts of Chemical Research, 1994, 27, 43. Texaphyrins and water-soluble texaphyrins and method of preparation have been described in U.S. Pat. Nos. 4,935,498; 5,252,720; 5,256,399; 5,272,142; and 5,292,414; and in international publn.s WO 94/29316 and WO 95/01996; all of which are incorporated herein by reference.
Sapphyrins and water-soluble sapphyrins and methods of preparation having been described in U.S. Pat. Nos. 5,041,078; 5,120,411; 5,159,065; and 5,302,714; and in International publn. WO 94/09994; all of which are incorporated herein by reference. Rubyrins are described in U.S. Pat. No. 5,410,045, incorporated herein by reference.